The higher the air temperature, the higher the saturated humidity. In medical science, there is a close relationship between air humidity and respiration. In an environment with relative humidity of 45 to 55%, oxygen can pass through the pulmonary alveoli and get into the blood relatively easy, thus when being in this kind of environment, the human body feel most comfortable. When being in an environment with high temperature and high humidity, the human body feels muggy since the perspiration function which regulates the body temperature is affected. In an environment with insufficient humidity, the human skin dries up easily and gets itchy; furthermore, the mucous membrane becomes stimulus-sensitive. In addition, air humidity control is very important for museums, libraries, manufacturing industry, building industry, alcohol-making industry, etc. In an environment with high humidity, moths, mold, termites, and microorganisms grow easily, and in an environment with insufficient humidity, the moisture content of objects excessively decreases, leading to damage such as stress variation, embrittlement, cracking, or warping.
Nevertheless, in prior art, the air-conditioning system, e.g., the central air-conditioning system, controls the air humidity degree by only providing either humidification or dehumidification, but not performs the humidification and dehumidification at the same time. Furthermore, the prior air-conditioning system is unable to be controlled via wired or wireless network. Some air conditioning systems even do not possess humidity monitoring mechanism, and is unable to turn off dehumidification function in time. Thus it is difficult for the air-conditioning system in prior art to satisfy different humidity requirements of different region, lack of practicality.